Spinal stenosis is the narrowing of the spinal cord canal, and can result in pain, weakness in arms and/or legs, and unsteadiness in the gait. For mild conditions, conservative treatment may be sufficient. When symptoms are severe or progressive, however, cervical laminoplasty surgery may be required to enlarge the spinal canal to relieve compression of the spinal cord. Common indications which give rise to a need for laminoplasty surgery include stenosis of the spinal canal, ossification of the posterior longitudinal ligament (OPLL), and spondylotic myelopathy.
Surgical techniques used to perform laminoplasty surgery can vary and will depend on many factors, including the source of the spinal cord compression, the number of vertebral segments involved in the disease process, and the cervical alignment. Two common surgical laminoplasty techniques include open door laminoplasty and midline splitting, or “French Door”, laminoplasty. In open door laminoplasty, the lamina is cut on one side and hinged on the other side. The lamina is then rotated to open the canal, and sutures are placed on the hinged side to maintain the opening, or a bone graft and/or plate is placed in the opening. Eventually, bone growth will fuse the hinge maintaining the open position. In French Door laminoplasty, both sides of the lamina are hinged, and the spinous process is bisected. Both halves are then rotated outwards, and a bone graft is placed between the halves to secure the opening.
Several devices exists for maintaining or stabilizing the lamina in the open or split position. U.S. Pat. No. 6,080,157 (Cathro), for example, discloses a device for stabilizing the lamina after open door laminoplasty surgery. The device includes a spacer which is shaped to engage between severed edges of a lamina, and a retainer attached to the spacer which is adapted to maintain the spacer in an operative position. U.S. Pat. No. 6,358,254 (Anderson) also discloses a device for expanding the spinal canal. The device includes two stents, two washers, two fasteners, and a cable. In use, pedicle cuts are made in the vertebra, and a fastener is then inserted into each cut, through a washer and a stent, to expand the cut bone. The cable is then attached to each washer and strapped around the posterior portion of the vertebrae to stabilize the expanded canal and allow the vertebrae to heal with the spinal canal expanded.
While these devices have proven effective, they can be difficult to implant, resulting in increased medical costs. Moreover, the devices do not have a substantially low-profile, and thus can potentially cause damage to surrounding tissue and/or to the spinal cord. The devices are also not designed to restore the natural dynamics of the cervical spine, and thus can cause discomfort to the patient.
Accordingly, there exists a need for an improved laminoplasty implant that is effective to maintain and stabilize the position of the lamina after laminoplasty surgery. Moreover, there is a need for a device that can be easily and safely implanted, that will allow for permanent bony incorporation when used with bone growth promoting materials, that will allow for muscle re-attachment, and that will restore the natural dynamics of the cervical spine.
US Published Patent Application U.S. 2002/0068975 (“Shaolian”) discloses formed in place orthopedic fixation devices comprising inflatable members inflated with hardenable media. Shaolian does not disclose hardenable media that is resorbable, osteoconductive, or osteoinductive. See also US Patent Publications 2002/0082598, US 2002/0082600, US2002/0198526, US 2004/0006341, US 2004/0006344 and U.S. Pat. No. 6,899,713, and PCT Patent Publication WO2003/020110.
U.S. Pat. No. 5,571,189 (“Kuslich”) discloses a flexible fabric bag packed with a biological fill composition that allows bone ingrowth through the bag. Kuslich further discloses a sausage-shaped container prefilled with fill composition and positioned against the bone of adjacent vertebrae. The containers become very rigid over time and attach via bone ingrowth to the vertebrae, ultimately to provide a fusion. In particular, in FIGS. 11 and 12 of Kuslich, a bag is depicted as a sausage-shaped container which is not implanted into a disc cavity. Rather, one or more of the bag containers, prefilled with fill composition are positioned against the bone of adjacent vertebrae. The bone may be toughened to a bleeding surface to hasten bone growth into the containers. According to Kuslich, as time goes by, the containers will become very rigid and will be attached via bone ingrowth to both vertebrae where they contact native bone to provide a safe, simple fusion. The bags provide containment of the bone-growth composition to ensure that the fusion takes place where indicated. Kuslich does not disclose a filled bag that is fixed to the adjacent vertebrae at the time of implantation. Accordingly, this device is subject is undesired movement prior to fusion.
PCT Patent Publication W00245765 (“Sybert”) disclosed an osteogenic band affixed to two or more vertebrae on the posterior side of the spine. Sybert does not disclose an in-situ hardenable composition.
U.S. Pat. No. 6,723,095 (Hammerslag) discloses methods of spinal fixation involving the application of a liquid medium which cures, hardens, polymerizes or otherwise serves to bind adjacent vertebrae together. Hammerslag discloses a preferred embodiment in which the liquid medium is a low viscosity cyanoacrylate-based adhesive, a composition that does not promote fusion. Although Hammerslag further teaches that “use of a medium to fix the articulate processes may be combined with methods which involve stimulating the growth of a bony mass or fusion body to fix the spine.” (7, 24-27), Hammerslag does not disclose fusion of the postero-lateral aspects of adjacent vertebrae.
US Patent Publication US2006-0004358 (Serhan) discloses in-situ formed spinal implant comprising a hardenable, resorbable, bone fusion-promoting composition, wherein the implant may be rigidly connected to adjacent vertebrae until fusion occurs.